Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.55	11.274%	$269.8951	$269.90	$269.90	$269.90
Purchase #2	$20.83	3.712%	$21.6032	$21.60	$21.60	$21.60
Purchase #3	$106.69	4.103%	$111.0675	$111.07	$111.05	$111.10
Purchase #4	$185.55	7.272%	$199.0432	$199.04	$199.05	$199.00
Purchase #5	$113.37	13.604%	$128.7929	$128.79	$128.80	$128.80
Purchase #6	$37.37	10.207%	$41.1844	$41.18	$41.20	$41.20
Purchase #7	$111.50	7.304%	$119.644	$119.64	$119.65	$119.60
7 purchase totals =	$817.86		$891.2303	$891.22	$891.25	$891.20